The present invention relates to a homopolar motor, and more particularly to a practical homopolar motor that is mated with a low voltage seawater activated battery to act as the power source of a scuba assist device.
The homopolar (acyclic, or Faraday) motor is fundamentally a high conductivity disk rotatable in a magnetic field. When current is applied between the shaft and rim of the disk, the current reacts with the magnetic field to produce a torque in the disk. The homopolar motor is also a low voltage, high current device, since the disk is essentially a one turn coil only, and disks cannot be connected in series for higher voltages without considerable difficulty. In the original version by Faraday, current was conducted into the rim of the disk at one restricted area where the disk dipped into a pool of mercury. A horseshoe magnet applied a magnetic flux across the current zone, between the pool and the shaft of the disk. The remainder of the disk did not contribute to the motor torque since it contained neither current nor magnetic flux.
Modern magnetic materials, such as ceramics, are capable of producing flux over the entire area of the disk, but then the current must also be introduced around the entire periphery of the disk. This peripheral current introduction is alimitation of past desings of homopolar motors: only a centrifugally maintained mercury ring or multiple brushes can be used to introduce the current. The centrifugal ring is impractical for units in mobile service or where there is frequent stopping and starting. Brushes must be applied to the highest velocity portion of the disk, so the friction, wear, vibration and arcing are very difficult to control.
A seawater battery is a unit in which each of the battery cells is immersed in an essentially infinite electrolytic volume. Since all of the cells are in the same volume of electrolyte, there are multiple leakage paths between all elements of the cells. The number of cells that can be connected in series is limited. The voltage of the battery is severely limited; the unit is a low voltage, high current, low impedance device. However, such a battery can provide the electrical requirements of a homopolar motor.